How do I work out when the bag is full?

[Himszy]

Hi,

I need to work out how full a bag is. I don't need exact measurements just
1/2 full 1/5 full ful empty etc. The bag is 2000cl and has water on the
outside with air on the inside.

What form of sensor do I need?

Thanks Michael

 

[JeffM]

I need to work out how full a bag is
...water on the outside with air on the inside.
Michael (Himszy)

Measure the bouyant force.
A pulley at the bottom and a spring scale out of the water.